The invention relates to a flexible sealing member for an injection device, comprising a neck, enclosing a channel diaphragm and having an annular flange at its closed end for a clamping connection of the sealing member in the injection device.
Such a sealing member is disclosed in British Patent Specification 1,318,803 and can be used in an injection device to separate the injection liquid in the barrel of said injection device from the injection needle. It is known to effect the communication between the barrel and the injection needle by causing the diaphragm to burst as a result of the fluid pressure exerted on the diaphragm after actuation of the device. As a result of this communication, the injection liquid in the barrel can reach the injection needle and will be injected.
Such sealing members can be used not only in manually operated injection devices, e.g. in prefilled injection devices, but also in automatic injection devices or auto injectors, e.g. in an autoinjector as disclosed in British Patent Specification 1,449,986. In fact, automatic injection devices are also pre-filled with injection liquid; they are, however, intended for use by unqualified persons. For that purpose they are constructed so that the injection liquid can be administered automatically by a person not trained in giving injections. Consequently, automatic injection devices are designed first of all for use by persons who at a given instant, which is not known beforehand, have to administer an injection into their own body. These persons include, for example, soldiers after they have been exposed to an enemy warfare gas, such as, a nerve gas. However, many of the medicaments used in automatic injection devices show undesired side effects or are insufficiently or incompletely active in therapeutic dosages. Therefore, the activity of said medicaments if often made up with benzodiazepines, for example diazepam, which is known to have a muscle-relaxing activity. In addition to said therapeutic activity, diazepam also has a sedative effect, as a result of which the fighting value of the soldiers at the front is restored. For this latter purpose the soldier in the field is preferably provided with a separate automatic injection device which is filled with a liquid diazepam formulation. Such an injector is especially intended for appeasing a buddy in the battle field who has panicked as a result of war acts or injuries: that is "buddy aid".
It will be obvious from the above, that high requirements regarding reliability have to be imposed upon automatic injection devices. Such injectors are usually stored for many years at a time and, moreover, will be kept by the potential users for long periods of time under varying conditions. Despite these facts, the reliability of the injector must be sufficiently ensured at the critical instant when the injection is required. In fact, at said critical instant the user's life may depend on the ready operation of the injection device. Therefore, high demands should be made upon the mechanical properties of a sealing member having a centrally positioned diaphragm which bursts under pressure and then permits the injection liquid to reach the injection needle. It will be obvious that said diaphragm should retain its sealing function prior to use of the injection device, but should burst open at the proper instant to allow passage of the injection liquid. These properties of the diaphragm should last, even under extreme conditions which may occur upon use of the device. The authorities even require a proper functioning of the injection device in the temperature range from -10.degree. C. up +50.degree. C., to permit use of the device under both arctic and tropical conditions.
It has been found, however, that an automatic injection device, provided with a sealing member as disclosed in British Patent Specification 1,318,803 mentioned hereinbefore, does not meet this requirement, in that at a temperature of -10.degree. C. the time required for ejecting the injection liquid is generally too long. The total time of ejection can be divided into the delay time, i.e. the time between actuation of the device and the start of liquid flow, and the real ejection time, i.e. the time between the start of liquid flow and the moment that said liquid flow has completely stopped. It has been observed, that in particular the delay time of this known injection device is completely unpredictable and varies between broad limits; therefore the "ejection-behavior" is not reproducible. This also applies when sealing members of bromobutyl rubber are used. This is the material of choice for injection devices comprising liquid diazepam formulations, as has been described in the non-prepublished European Patent Application no. 90200587.5 in the name of Applicants.